9,350 research outputs found
Correlation Induced Insulator to Metal Transitions
We study a spinless two-band model at half-filling in the limit of infinite
dimensions. The ground state of this model in the non-interacting limit is a
band-insulator. We identify transitions to a metal and to a charge-Mott
insulator, using a combination of analytical, Quantum Monte Carlo, and zero
temperature recursion methods. The metallic phase is a non-Fermi liquid state
with algebraic local correlation functions with universal exponents over a
range of parameters.Comment: 12 pages, REVTE
Effect of conduction electron interactions on Anderson impurities
The effect of conduction electron interactions for an Anderson impurity is
investigated in one dimension using a scaling approach. The flow diagrams are
obtained by solving the renormalization group equations numerically. It is
found that the Anderson impurity case is different from its counterpart -- the
Kondo impurity case even in the local moment region. The Kondo temperature for
an Anderson impurity shows nonmonotonous behavior, increasing for weak
interactions but decreasing for strong interactions. The implication of the
study to other related impurity models is also discussed.Comment: 10 pages, revtex, 4 figures (the postscript file is included), to
appear in Phys. Rev. B (Rapid Commun.
Kosterlitz-Thouless Transition and Short Range Spatial Correlations in an Extended Hubbard Model
We study the competition between intersite and local correlations in a
spinless two-band extended Hubbard model by taking an alternative limit of
infinite dimensions. We find that the intersite density fluctuations suppress
the charge Kondo energy scale and lead to a Fermi liquid to non-Fermi liquid
transition for repulsive on-site density-density interactions. In the absence
of intersite interactions, this transition reduces to the known
Kosterlitz-Thouless transition. We show that a new line of non-Fermi liquid
fixed points replace those of the zero intersite interaction problem.Comment: 11 pages, 2 figure
Coarse-to-fine classification of road infrastructure elements from mobile point clouds using symmetric ensemble point network and euclidean cluster extraction
Classifying point clouds obtained from mobile laser scanning of road environments is a fundamental yet challenging problem for road asset management and unmanned vehicle navigation. Deep learning networks need no prior knowledge to classify multiple objects, but often generate a certain amount of false predictions. However, traditional clustering methods often involve leveraging a priori knowledge, but may lack generalisability compared to deep learning networks. This paper presents a classification method that coarsely classifies multiple objects of road infrastructure with a symmetric ensemble point (SEP) network and then refines the results with a Euclidean cluster extraction (ECE) algorithm. The SEP network applies a symmetric function to capture relevant structural features at different scales and select optimal sub-samples using an ensemble method. The ECE subsequently adjusts points that have been predicted incorrectly by the first step. The experimental results indicate that this method effectively extracts six types of road infrastructure elements: road surfaces, buildings, walls, traffic signs, trees and streetlights. The overall accuracy of the SEP-ECE method improves by 3.97% with respect to PointNet. The achieved average classification accuracy is approximately 99.74%, which is suitable for practical use in transportation network management
Quantum Chemistry, Anomalous Dimensions, and the Breakdown of Fermi Liquid Theory in Strongly Correlated Systems
We formulate a local picture of strongly correlated systems as a Feynman sum
over atomic configurations. The hopping amplitudes between these atomic
configurations are identified as the renormalization group charges, which
describe the local physics at different energy scales. For a metallic system
away from half-filling, the fixed point local Hamiltonian is a generalized
Anderson impurity model in the mixed valence regime. There are three types of
fixed points: a coherent Fermi liquid (FL) and two classes of self-similar
(scale invariant) phases which we denote incoherent metallic states (IMS). When
the transitions between the atomic configurations proceed coherently at low
energies, the system is a Fermi liquid. Incoherent transitions between the low
energy atomic configurations characterize the incoherent metallic states. The
initial conditions for the renormalization group flow are determined by the
physics at rather high energy scales. This is the domain of local quantum
chemistry. We use simple quantum chemistry estimates to specify the basin of
attraction of the IMS fixed points.Comment: 12 pages, REVTE
Global Phase Diagram of the Kondo Lattice: From Heavy Fermion Metals to Kondo Insulators
We discuss the general theoretical arguments advanced earlier for the T=0
global phase diagram of antiferromagnetic Kondo lattice systems, distinguishing
between the established and the conjectured. In addition to the well-known
phase of a paramagnetic metal with a "large" Fermi surface (P_L), there is also
an antiferromagnetic phase with a "small" Fermi surface (AF_S). We provide the
details of the derivation of a quantum non-linear sigma-model (QNLsM)
representation of the Kondo lattice Hamiltonian, which leads to an effective
field theory containing both low-energy fermions in the vicinity of a Fermi
surface and low-energy bosons near zero momentum. An asymptotically exact
analysis of this effective field theory is made possible through the
development of a renormalization group procedure for mixed fermion-boson
systems. Considerations on how to connect the AF_S and P_L phases lead to a
global phase diagram, which not only puts into perspective the theory of local
quantum criticality for antiferromagnetic heavy fermion metals, but also
provides the basis to understand the surprising recent experiments in
chemically-doped as well as pressurized YbRh2Si2. We point out that the AF_S
phase still occurs for the case of an equal number of spin-1/2 local moments
and conduction electrons. This observation raises the prospect for a global
phase diagram of heavy fermion systems in the Kondo-insulator regime. Finally,
we discuss the connection between the Kondo breakdown physics discussed here
for the Kondo lattice systems and the non-Fermi liquid behavior recently
studied from a holographic perspective.Comment: (v3) leftover typos corrected. (v2) Published version. 32 pages, 4
figures. Section 7, on the connection between the Kondo lattice systems and
the holographic models of non-Fermi liquid, is expanded. (v1) special issue
of JLTP on quantum criticalit
Magnetotransport near a quantum critical point in a simple metal
We use geometric considerations to study transport properties, such as the
conductivity and Hall coefficient, near the onset of a nesting-driven spin
density wave in a simple metal. In particular, motivated by recent experiments
on vanadium-doped chromium, we study the variation of transport coefficients
with the onset of magnetism within a mean-field treatment of a model that
contains nearly nested electron and hole Fermi surfaces. We show that most
transport coefficients display a leading dependence that is linear in the
energy gap. The coefficient of the linear term, though, can be small. In
particular, we find that the Hall conductivity is essentially
unchanged, due to electron-hole compensation, as the system goes through the
quantum critical point. This conclusion extends a similar observation we made
earlier for the case of completely flat Fermi surfaces to the immediate
vicinity of the quantum critical point where nesting is present but not
perfect.Comment: 11 pages revtex, 4 figure
Strong and nearly 100 spin-polarized second-harmonic generation from ferrimagnet MnRuGa
Second-harmonic generation (SHG) has emerged as a promising tool for
detecting electronic and magnetic structures in noncentrosymmetric materials,
but 100 spin-polarized SHG has not been reported. In this work, we
demonstrate nearly 100 spin-polarized SHG from half-metallic ferrimagnet
MnRuGa. A band gap in the spin-down channel suppresses SHG, so the
spin-up channel contributes nearly all the signal, as large as 3614 pm/V about
10 times larger than that of GaAs. In the spin-up channel,
is dominated by the large intraband current in three highly dispersed bands
near the Fermi level. With the spin-orbit coupling (SOC), the reduced magnetic
point group allows additional SHG components, where the interband contribution
is enhanced. Our finding is important as it predicts a large and complete
spin-polarized SHG in a all-optical spin switching ferrimagnet. This opens the
door for future applications
Kondo Insulator to Semimetal Transformation Tuned by Spin-Orbit Coupling
Recent theoretical studies of topologically nontrivial electronic states in
Kondo insulators have pointed to the importance of spin-orbit coupling (SOC)
for stabilizing these states. However, systematic experimental studies that
tune the SOC parameter in Kondo insulators remain elusive.
The main reason is that variations of (chemical) pressure or doping strongly
influence the Kondo coupling and the chemical potential --
both essential parameters determining the ground state of the material -- and
thus possible tuning effects have remained unnoticed. Here
we present the successful growth of the substitution series
CeBi(PtPd) () of the archetypal
(noncentrosymmetric) Kondo insulator CeBiPt. The Pt-Pd substitution
is isostructural, isoelectronic, and isosize, and therefore likely to leave
and essentially unchanged. By contrast, the large mass
difference between the element Pt and the element Pd leads to a large
difference in , which thus is the dominating tuning
parameter in the series. Surprisingly, with increasing (decreasing
), we observe a Kondo insulator to semimetal transition,
demonstrating an unprecedented drastic influence of the SOC. The fully
substituted end compound CeBiPd shows thermodynamic signatures of a
recently predicted Weyl-Kondo semimetal.Comment: 6 pages, 5 figures plus Supplemental Materia
The suppression of hidden order and onset of ferromagnetism in URu2Si2 via Re substitution
Substitution of Re for Ru in the heavy fermion compound URu2Si2 suppresses
the hidden order transition and gives rise to ferromagnetism at higher
concentrations. The hidden order transition of URu(2-x)Re(x)Si2, tracked via
specific heat and electrical resistivity measurements, decreases in temperature
and broadens, and is no longer observed for x>0.1. A critical scaling analysis
of the bulk magnetization indicates that the ferromagnetic ordering temperature
and ordered moment are suppressed continuously towards zero at a critical
concentration of x = 0.15, accompanied by the additional suppression of the
critical exponents gamma and (delta-1) towards zero. This unusual trend appears
to reflect the underlying interplay between Kondo and ferromagnetic
interactions, and perhaps the proximity of the hidden order phase.Comment: 8 pgs, 5 figs, ICM 2009; please refer to Phys. Rev. Lett. 103, 076404
(2009), arXiv:0908.1809 for details on magnetic scaling and phase diagram
(reference added to this version
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